fixing the zero division bug in mixture_smoothing.py
fixing the zero division bug in mixture_smoothing.py

pastephens/pysal,badjr/pysal,schmidtc/pysal,lixun910/pysal,dfolch/pysal,lanselin/pysal,jlaura/pysal,jlaura/pysal,darribas/pysal,sjsrey/pysal_core,hasecbinusr/pysal,sjsrey/pysal_core,ljwolf/pysal,chhao91/pysal,schmidtc/pysal,ljwolf/pysal,TaylorOshan/pysal,hasecbinusr/pysal,ljwolf/pysal,lixun910/pysal,ljwolf/pysal_core,darribas/pysal,pastephens/pysal,pedrovma/pysal,spreg-git/pysal,pastephens/pysal,lixun910/pysal,TaylorOshan/pysal,pysal/pysal,jlaura/pysal,weikang9009/pysal,ljwolf/pysal_core,spreg-git/pysal,ljwolf/pysal_core,chhao91/pysal,nathania/pysal,TaylorOshan/pysal,hasecbinusr/pysal,sjsrey/pysal_core,nathania/pysal,sjsrey/pysal,dfolch/pysal,badjr/pysal